code: def add_subparser(
      self, parser: argparse._SubParsersAction
  ) -> argparse.ArgumentParser:
      description = """Display a diff between two model checkpoints."""
      long_description = (
          description
          + """
          In the output, lines start with either a "+", "-", "!", or empty space " ".
          "+" means the corresponding parameter is present in the 2nd checkpoint but not the 1st.
          "-" means the corresponding parameter is present in the 1st checkpoint but not the 2nd.
          "!" means the corresponding parameter is present in both, but has different weights (same shape)
          according to the distance calculation and the '--threshold' value.
          And " " means the corresponding parameter is considered identical in both, i.e.
          the distance falls below the threshold.
          The distance between two tensors is calculated as the root of the
          mean squared difference, multiplied by the '--scale' parameter.
          """
      )
      subparser = parser.add_parser(
          self.name,
          description=long_description,
          help=description,
      )
      subparser.set_defaults(func=_diff)
      subparser.add_argument(
          "checkpoint1",
          type=str,
          help="""the URL, path, or other identifier (see '--checkpoint-type-1')
              to the 1st PyTorch checkpoint.""",
      )
      subparser.add_argument(
          "checkpoint2",
          type=str,
          help="""the URL, path, or other identifier (see '--checkpoint-type-2')
              to the 2nd PyTorch checkpoint.""",
      )
      subparser.add_argument(
          "--strip-prefix-1",
          type=str,
          help="""a prefix to remove from all of the 1st checkpoint's keys.""",
      )
      subparser.add_argument(
          "--strip-prefix-2",
          type=str,
          help="""a prefix to remove from all of the 2nd checkpoint's keys.""",
      )
      subparser.add_argument(
          "--scale",
          type=float,
          default=1.0,
          help="""controls the scale of the distance calculation.""",
      )
      subparser.add_argument(
          "--threshold",
          type=float,
          default=1e-5,
          help="""the threshold for the distance between two tensors,
              under which the two tensors are considered identical.""",
      )
      return subparser
  
imports: import argparse
  import logging
  from typing import Union, Dict, List, Tuple, NamedTuple, cast
  import termcolor
  import torch
  from allennlp.commands.subcommand import Subcommand
  from allennlp.common.file_utils import cached_path
  from allennlp.nn.util import read_state_dict
label_desc: Use image node_id 1 for calling the Diff obj's underlying member method code with example usage: obj.add_subparser(parser) and returns: subparser